23_a_3: Add solution

1 files changed, 17 insertions, 0 deletions

diff --git a/ch23/23_a_3.hs b/ch23/23_a_3.hs
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+-- Why does guiFetch combine worker functions instead of calling statusWindow
+-- twice?
+
+
+-- The most important reason is: Considering how the operations are implemented,
+-- updating the podcast and downloading its episodes need to be run sequentially
+-- in that order because the downloading can produce expected results only when
+-- it knows the latest information about the podcast's episodes.
+--
+-- Calling statusWindow twice would run those operations concurrently and their
+-- execution ordering could not be predicted. For example, the downloading could
+-- be run before the updating.
+--
+-- Other than that, the statusWindow uses the same GUI status window. The latter
+-- call to it would overwrite information from the former call, replacing the
+-- callback for canceling the child thread. Then it wouldn't be possible for the
+-- user to cancel the first thread.